Hand grenades are an ancient weapon but hardly irrelevant. There are few devices as brutally effective at killing inside enclosed spaces, such as caves or rooms, than a device such as the U.S. Army’s M67 fragmentation grenade.
The M67 has been around for awhile, being first introduced into service in 1968. And mechanically, it’s little different from the grenades American soldiers lobbed into bunkers during the World Wars. It’s a relic, one still quite practical and useful, that has survived like the M2 Browning machine gun into the 21st century.